$min and $max update operators in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the document after applying $min update?

Given the document

{ "_id": 1, "score": 50 }

and the update operation

{ "$min": { "score": 40 } }

, what will be the value of score after the update?

MongoDB

db.collection.updateOne({ _id: 1 }, { $min: { score: 40 } })
db.collection.findOne({ _id: 1 })

A { "_id": 1, "score": 40 }

B { "_id": 1, "score": null }

C { "_id": 1, "score": 90 }

D { "_id": 1, "score": 50 }

💡 Hint

The $min operator updates the field only if the specified value is less than the current value.

The $min operator updates the field only if the new value is less than the current value. Since 40 is less than 50, the score is updated to 40.

❓ query_result

intermediate

What is the document after applying $max update?

Given the document

{ "_id": 2, "level": 10 }

and the update operation

{ "$max": { "level": 15 } }

, what will be the value of level after the update?

MongoDB

db.collection.updateOne({ _id: 2 }, { $max: { level: 15 } })
db.collection.findOne({ _id: 2 })

A { "_id": 2, "level": 15 }

B { "_id": 2, "level": 10 }

C { "_id": 2, "level": 5 }

D { "_id": 2, "level": null }

💡 Hint

The $max operator updates the field only if the specified value is greater than the current value.

The $max operator updates the field only if the new value is greater than the current value. Since 15 is greater than 10, the level is updated to 15.

📝 Syntax

advanced

Which update operation is syntactically correct to use $min on nested field?

You want to update the nested field stats.score to 30 only if 30 is less than the current value. Which of the following update operations is correct?

A { "$min": { "stats": { "score": 30 } } }

B { "$min": { stats: { score: 30 } } }

C { "$min": { "stats.score": 30 } }

D { "$min": { "stats->score": 30 } }

💡 Hint

Use dot notation to update nested fields in MongoDB.

MongoDB uses dot notation to specify nested fields in update operations. Option C correctly uses "stats.score" as the field name.

❓ query_result

advanced

What happens if $max is used with a value less than current field value?

Given the document

{ "_id": 3, "points": 100 }

and the update

{ "$max": { "points": 80 } }

, what will be the value of points after the update?

MongoDB

db.collection.updateOne({ _id: 3 }, { $max: { points: 80 } })
db.collection.findOne({ _id: 3 })

A { "_id": 3, "points": 80 }

B Update operation fails with error

C { "_id": 3, "points": null }

D { "_id": 3, "points": 100 }

💡 Hint

The $max operator only updates if the new value is greater than the current value.

The $max operator updates the field only if the new value is greater than the current value. Since 80 is less than 100, the field remains unchanged.

🧠 Conceptual

expert

Why would you use $min and $max operators in a leaderboard system?

In a game leaderboard, you want to keep track of the highest and lowest scores a player has achieved. Which statement best explains why $min and $max operators are useful here?

A $min and $max operators automatically sort the leaderboard by scores.

B $min and $max allow atomic updates to keep track of lowest and highest scores without reading the document first.

C $min and $max operators create new fields for lowest and highest scores automatically.

D $min and $max operators delete scores that are not minimum or maximum.

💡 Hint

Think about how to update values safely when multiple users might update scores at the same time.

The $min and $max operators allow atomic updates to a field only if the new value is less or greater respectively. This avoids race conditions and the need to read the document before updating.